1. Field of the Invention
The invention is directed to a power semiconductor substrate and a method of manufacturing such a substrate, more particularly, to such a power semiconductor substrate in which a layer of a metallic material is applied to a contact area thereof.
2. Description of the Related Art
The invention relates to power semiconductor substrates that include an insulating base body, at least one conductor track and at least one contact area of one of said conductor tracks. Power semiconductor substrates of this type are known by way of example as AMD (active metal braze), DCB (direct copper bonding) or IMS (insulated metal substrate) substrates.
The contact area, as part or section of a conductor track, provides an electrically conductive connection, for example, to power semiconductor components or to external connections. Connecting elements of this type may, for example, be formed with the contact area by soldering connections or pressure-contact-connected connections. Connections with contact springs are of particular interest here especially in the case of pressure-contact-connected connections.
In accordance with the prior art, DCB substrates are known which comprise a ceramic base, often aluminium oxide or aluminium nitride, with conductor tracks composed of a copper film arranged thereon. Conductor tracks of this type are preferred for soldering connections and in this case form the contact area themselves. It is likewise known to form some or all of the contact areas with an additional thin layer of gold, preferably having a thickness of a few (no more than 15) atomic layers. This is advantageous particularly for contact areas of wire bonding connections. These contact areas are not sufficient in conjunction with pressure-contact-connected terminal elements, such as auxiliary or load terminal elements of power semiconductor modules, which can be formed as contact springs in accordance with the prior art. As a result of the thermal loading and the application of pressure, the contact feet of the contact springs can damage the thin layer of gold and therefore impair the reliability of the contact.